Synaptic lipid signaling: significance of polyunsaturated fatty acids and platelet-activating factor

Oxidized phospholipid: POVPC binds to platelet-activating-factor receptor on human macrophages. Implications in atherosclerosis

Atherosclerosis as a chronic inflammatory disease resulting from the imbalance of the pro- and anti-inflammatory factors in the vessel wall. PAF and PAF-like oxidized phospholipids generated upon LDL oxidation in the intima of the arteries may interact with infiltrated monocytes/macrophages and lead to the alteration of gene expression patterns accompanied by an impaired production of chemokines, interleukins and proteolytic and lipolytic enzymes. The aim of this study was to evaluate the binding capacity of the major component of PAF-like oxidized phospholipids, namely the 1-palmitoyl-2-oxovaleroyl-sn-glycero-3-phosphorylcholine (POVPC) to PAF-receptor (PAF-R) on the surface of human monocytes/macrophages and to further characterize the gene expression induced by such binding. We show that, POVPC binds to cultured human macrophages via PAF-R and transduces the signals leading to the intracellular Ca(2+) fluxes and modifies the transcription levels of numerous pro-inflammatory and pro-atherogenic genes. Although a some similarity of the gene expression patterns was observed when macrophages were activated with POVPC versus PAF, we observed that only POVPC treatment induced a several-fold activation of IL-8 gene. In turn, only PAF activated PAF-R, matrix metalloproteinase-13 and 15-lipoxygenase mRNA accumulation. Thus, we suggest, that POVPC signals in mature macrophages only in part through the PAF-R, a part of its effects may involve other receptors.

Lipid signaling: sleep, synaptic plasticity, and neuroprotection

Increasing evidence indicates that bioactive lipids participate in the regulation of synaptic function and dysfunction. We have demonstrated that signaling mediated by platelet-activating factor (PAF) and cyclooxygenase (COX)-2-synthesized PGE2 is involved in synaptic plasticity, memory, and neuronal protection [Clark GD, Happel LT, Zorumski CF, Bazan NG. Enhancement of hippocampal excitatory synaptic transmission by platelet-activating factor. Neuron 1992; 9:1211; Kato K, Clark GD, Bazan NG, Zorumski CF. Platelet-activating factor as a potential retrograde messenger in CA1 hippocampal long-term potentiation. Nature 1994; 367:175; Izquierdo I, Fin C, Schmitz PK, et al. Memory enhancement by intrahippocampal, intraamygdala or intraentorhinal infusion of platelet-activating factor measured in an inhibitory avoidance. Proc Natl Acad Sci USA 1995; 92:5047; Chen C, Magee CJ, Bazan NG. Cyclooxygenase-2 regulates prostaglandin E2 signaling in hippocampal long-term synaptic plasticity. J Neurophysiol 2002; 87:2851]. Recently, we found that prolonged continuous wakefulness (primarily rapid eye movement (REM)-sleep deprivation, SD) causes impairments in hippocampal long-term synaptic plasticity and hippocampus-dependent memory formation [McDermott CM, LaHoste GJ, Chen C, Musto A, Bazan NG, Magee JC. Sleep deprivation causes behavioral, synaptic, and membrane excitability alterations in hippocampal neurons. J Neurosci 2003; 23:9687]. To explore the mechanisms underlying SD-induced impairments, we have studied several bioactive lipids in the hippocampus following SD. It appears that SD causes increases in prostaglandin D2 (PGD2) and 2-arachidonylglycerol (2-AG), and a decrease in PGE2, suggesting that these lipid messengers participate in memory consolidation during REM sleep. We have also explored the formation of endogenous neuroprotective lipids. Toward this aim, we have used ischemia-reperfusion damage and LC-PDA-ESI-MS-MS-based lipidomic analysis and identified docosanoids derived from synaptic phospholipid-enriched docosahexaenoic acid. Some of the docosanoids exert potent neuroprotective bioactivity [Marcheselli VL, Hong S, Lukiw WJ, et al. Novel docosanoids inhibit brain ischemia-reperfusion-mediated leukocyte infiltration and pro-inflammatory gene expression. J Biol Chem 2003; 278:43807; Mukherjee PK, Marcheselli VL, Serhan CN, Bazan, NG. Neuroprotectin D1: A docosahexaenoic acid-derived docosatriene protects human retinal pigment epithelial cells from oxidative stress. Proc Nat Acad Sci USA 2004; 101:8491). Taken together, these observations that signaling lipids participate in synaptic plasticity, cognition, and survival indicate that lipid signaling is closely associated with several functions (e.g; learning and memory, sleep, and experimental stroke) and pathologic events. Alterations in endogenous signaling lipids or their receptors resulting from drug abuse lead to changes in synaptic circuitry and induce profound effects on these important functions. In the present article, we will briefly review bioactive lipids involved in sleep, synaptic transmission and plasticity, and neuroprotection, focusing mainly on our experimental studies and how these signaling molecules are related to functions and implicated in some neurologic disorders.

A role for docosahexaenoic acid-derived neuroprotectin D1 in neural cell survival and Alzheimer disease

Deficiency in docosahexaenoic acid (DHA), a brain-essential omega-3 fatty acid, is associated with cognitive decline. Here we report that, in cytokine-stressed human neural cells, DHA attenuates amyloid-beta (Abeta) secretion, an effect accompanied by the formation of NPD1, a novel, DHA-derived 10,17S-docosatriene. DHA and NPD1 were reduced in Alzheimer disease (AD) hippocampal cornu ammonis region 1, but not in the thalamus or occipital lobes from the same brains. The expression of key enzymes in NPD1 biosynthesis, cytosolic phospholipase A2 and 15-lipoxygenase, was altered in AD hippocampus. NPD1 repressed Abeta42-triggered activation of proinflammatory genes while upregulating the antiapoptotic genes encoding Bcl-2, Bcl-xl, and Bfl-1(A1). Soluble amyloid precursor protein-alpha stimulated NPD1 biosynthesis from DHA. These results indicate that NPD1 promotes brain cell survival via the induction of antiapoptotic and neuroprotective gene-expression programs that suppress Abeta42-induced neurotoxicity.

Nutritional aspects modulating brain development and the responses to stress in early neonatal life

Nutrition is one of the critical factors insuring adequate growth and development in all species. In particular, brain development is sensitive to specific nutrient intake such as proteins and lipids, which are important for cell membrane formation and myelinization. Carbohydrate intake insures adequate short-term energy supply, but has important effects on the activity of the hypothalamic-pituitary-adrenal (HPA) axis to regulate stress responsiveness. This review focuses on the effects of carbohydrates and fat on the activity of the HPA axis as well as other brain-related functions such as pain modulation, neuropeptide and neurotransmitters release, and some aspects related to cognitive functions. The role of leptin, DHA and AA as mediators of the effects of fat on the brain is discussed.

Calcium Signals Activated by Arachidonic Acid in Embryonic Chick Ciliary Ganglion Neurons

Arachidonic acid (AA, 20:4) has been reported to modulate a variety of calcium-permeable ionic channels, both in the plasma membrane and in the endoplasmic reticulum. We have studied the effects of AA on calcium signaling in a well-characterized model of developing peripheral neurons, embryonic chick ciliary ganglion neurons in culture. When given at low non-micellar concentrations (5 microM), in the majority of cells AA directly activated a delayed and long-lasting increase in [Ca2+]i, involving both the cytoplasm and the nucleoplasm, that was completely reversed by abolition of extracellular calcium. Other fatty acids (FAs), either saturated like arachidic acid (20:0), or unsaturated like linoleic (18:2) and docosahexaenoic acid (22:6), shared its ability to activate calcium influx. This entry was not suppressed by voltage-dependent calcium channel inhibitors omega-conotoxin and nifedipine, by the voltage-independent calcium channel antagonist LOE-908, by pre-treatment with blockers of AA metabolic pathways or with pertussis toxin. The arachidonate-activated calcium pathway was permeable to Mn2+ and blocked by La3+, Gd3+ and Ni2+. In a neuronal subpopulation, AA at the same concentration was also able to elicit calcium release from thapsigargin-sensitive intracellular stores; we provide evidence that cytochrome P450 epoxygenase is involved in this process.

Lipid signaling in neural plasticity, brain repair, and neuroprotection

The extensive networking of the cells of the nervous system results in large cell membrane surface areas. We now know that neuronal membranes contain phospholipid pools that are the reservoirs for the synthesis of specific lipid messengers on neuronal stimulation or injury. These messengers in turn participate in signaling cascades that can either promote neuronal injury or neuroprotection. Prostaglandins are synthesized as a result of cyclooxygenase activity. In the first step of the arachidonic acid cascade, the short-lived precursor, prostaglandin H2, is synthesized. Additional steps in the cascade result in the synthesis of an array of prostaglandins, which participate in numerous physiological and neurological processes. Our laboratory recently reported that the membrane polyunsaturated fatty acid, docosahexaenoic acid, is the precursor of oxygenation products now known as the docosanoids, some of which are powerful counter-proinflammatory mediators. The mediator 10,17S-docosatriene (neuroprotectin D1, NPD1) counteracts leukocyte infiltration, NF-kappa activation, and proinflammatory gene expression in brain ischemia-reperfusion and is an apoptostatic mediator, potently counteracting oxidative stress-triggered apoptotic DNA damage in retinal pigment epithelial cells. NPD1 also upregulates the anti-apoptotic proteins Bcl-2 and Bcl-xL and decreases pro-apoptotic Bax and Bad expression. Another biologically active messenger derived from membrane phospholipids in response to synaptic activity is platelet-activating factor (PAF). The tight regulation of the balance between synthesis (via phospholipases) and degradation (via acetylhydrolases) of PAF modulates the functions of this lipid messenger. Under pathological conditions, this balance is tipped, and PAF becomes a proinflammatory mediator and neurotoxic agent. The newly discovered docosahexaenoic acid signaling pathways, as well as other lipid messengers related to synaptic activation, may lead to the clarification of clinical issues relevant to stroke, age-related macular degeneration, spinal cord injury, Alzheimer's disease, and other diseases that include neuroinflammatory components.

(n-3) polyunsaturated fatty acid deficiency reduces the expression of both isoforms of the brain glucose transporter GLUT1 in rats

The altered neuron activity of rats deficient in (n-3) PUFAs may be due in part to a decrease in brain glucose utilization and glucose transport. We measured the glucose transporter protein GLUT1 isoforms at the blood-brain barrier (55-kDa) and in astrocytes (45-kDa) by Western immunoblotting and their mRNA by real time RT-PCR analysis in the cerebral cortex of adult male rats fed diets lacking (n-3) fatty acids (1st generation). The neuron glucose transporter GLUT3 was also assayed. The fatty acids in the phosphatidylcholine (PC), ethanolamine phosphoglycerolipid (EPG), and phosphatidylserine (PS) fractions of isolated microvessels and homogenates of the cerebral cortex were determined. The levels of (n-6) PUFAs [mainly arachidonic acid, 20:4(n-6)] in the phospholipid fractions of microvessels were higher and the levels of (n-3) PUFAs [mainly docosahexaenoic acid, 22:6(n-3)] were lower than in cerebral cortex homogenates. The microvessels and cortex of rats fed the (n-3) PUFA-deficient diet had 50% of the control 22:6(n-3) contents; 22:6(n-3) was replaced by 22:5(n-6). The 55-kDa GLUT1 immunoreactivity in (n-3) PUFA-deficient microvessels was decreased (down 25%, P < 0.01), as was the 45 kDa-GLUT1 in the homogenate (down 30%, P < 0.01). But the amount of immunoreactivity of GLUT3 did not change. The amount of GLUT1 mRNA was not affected by the (n-3) PUFA-deficient diet. These results suggest that the decreased glucose utilization in the cerebral cortex of (n-3) PUFA-deficient rats is due to reduced amounts of the 2 isoforms of GLUT1, indicating post-transcriptional regulation of GLUT1 synthesis.

The potential role of sigma-1 receptors in lipid transport and lipid raft reconstitution in the brain: implication for drug abuse

The brain is highly enriched in lipids. However, the molecular biological roles of lipids in the brain have been largely unexplored. Although, in 1990s, several studies have demonstrated the roles of lipids in a variety of neuronal functions and certain neurological diseases, the involvement of lipids in drug dependence, if any, is almost totally unknown. Sigma-1 receptors are brain-enriched proteins that interact with psychostimulants such as cocaine and methamphetamine. Sigma-1 receptors possess a putative sterol-binding pocket and are predominantly expressed on the endoplasmic reticulum (ER) where most lipids and their precursors are synthesized. Sigma-1 receptors are involved in drug-seeking behaviors and in psychostimulant-induced behavioral sensitization. Recent studies demonstrated that sigma-1 receptors target the lipid-storing subcompartments of the ER and are colocalized with cholesterol and neutral lipids. Sigma-1 receptors form detergent-insoluble lipid microdomains (lipid rafts) on the ER subcompartments and can translocate on the ER when stimulated. Upregulation of sigma-1 receptors affect the levels of plasma membrane lipid rafts by changing the lipid components therein. The membrane reconstitution thus induced by sigma-1 receptors in turn affects functions of proteins residing in plasma membrane lipid rafts including tropic factor receptors and tyrosine kinases. Specifically, we recently found that sigma-1 receptors modulate MAP kinase activation induced by tropic factors, neuritegenesis and oligodendrocyte differentiation-all related to lipid raft reconstitution. Sigma-1 receptors may thus play a role in psychostimulant-induced long-lasting morphological changes in the brain via the capacity of sigma-1 receptors in regulating ER lipid transport and the resultant plasma membrane lipid raft reconstitution.

Postsynaptic IP3 receptor-mediated Ca2+ release modulates synaptic transmission in hippocampal neurons

Ca(2+)-dependent mechanisms are important in regulating synaptic transmission. The results herein indicate that whole-cell perfusion of inositol 1,4,5-trisphosphate receptor (IP(3)R) agonists greatly enhanced excitatory postsynaptic current (EPSC) amplitudes in postsynaptic hippocampal CA1 neurons. IP(3)R agonist-mediated increases in synaptic transmission changed during development and paralleled age-dependent increases in hippocampal type-1 IP(3)Rs. IP(3)R agonist-mediated increases in EPSC amplitudes were inhibited by postsynaptic perfusion of inhibitors of Ca(2+)/calmodulin, PKC and Ca(2+)/calmodulin-dependent protein kinase II. Postsynaptic perfusion of inhibitors of smooth endoplasmic reticulum (SER) Ca(2+)-ATPases, which deplete intracellular Ca(2+) stores, also enhanced EPSC amplitudes. Postsynaptic perfusion of the IP(3)R agonist adenophostin (AdA) during subthreshold stimulation appeared to convert silent to active synapses; synaptic transmission at these active synapses was completely blocked by 6-cyano-7-nitroquinoxaline-2,3-dione (CNQX). Postsynaptic IP(3)R-mediated Ca(2+) release also produced a significant increase in spontaneous EPSC frequency. These results indicate that Ca(2+) release from intracellular stores play a key role in regulating the function of postsynaptic AMPARs.

Dietary docosahexaenoic acid [22: 6(n-3)] as a phospholipid or a triglyceride enhances the potassium chloride-evoked release of acetylcholine in rat hippocampus

We demonstrated previously that a dietary-induced depletion of docosahexaenoic acid (DHA) in cerebral phospholipids increases the spontaneous release of acetylcholine (Ach) in the rat hippocampus and reduces its potassium chloride evoked-release. In the present study, we investigated the effects in rats of DHA-enriched diets supplied by egg phospholipids (E-PL) or tuna oil (TO) on the PUFA in hippocampus membranes and on the synaptic release of Ach. Control rats were fed 3 g/kg of the DHA precursor, alpha-linolenic acid (LNA). Chronically (n-3) PUFA-deficient females were fed, starting 2 wk before mating, the deficient diet, a control diet, or a purified diet supplying 1, 2, or 3 g DHA/kg diet as E-PL or TO. Experiments were performed on the adult male progeny fed the same diet as their dams throughout life. The form of dietary DHA (TO or E-PL) did not influence its incorporation into the hippocampus. The 1 g DHA/kg diets allowed maximal incorporation into phosphatidylethanolamine (PE), but 2 g DHA/kg diet was needed for phosphatidylcholine (PC). A minimum of 2 g DHA/kg was needed to decrease the basal Ach release and to enhance the stimulated release to that of the control; the Ach release of the 1 g/kg DHA-groups did not differ from that of the deficient group. This suggests that >1 g DHA/kg diet is needed to ensure PUFA incorporation into PE and PC, and basal and stimulated Ach release in the rat hippocampus equivalent to the control group fed only LNA. PUFA incorporation into the hippocampus depends mainly on the PUFA concentration of the diet, not on the form of dietary DHA.

Neuroprotectin D1 (NPD1): a DHA-derived mediator that protects brain and retina against cell injury-induced oxidative stress

The biosynthesis of oxygenated arachidonic acid messengers triggered by cerebral ischemia-reperfusion is preceded by an early and rapid phospholipase A2 activation reflected in free arachidonic and docosahexaenoic acid (DHA) accumulation. These fatty acids are released from membrane phospholipids. Both fatty acids are derived from dietary essential fatty acids; however, only DHA, the omega-3 polyunsaturated fatty acyl chain, is concentrated in phospholipids of various cells of brain and retina. Synaptic membranes and photoreceptors share the highest content of DHA of all cell membranes. DHA is involved in memory formation, excitable membrane function, photoreceptor cell biogenesis and function, and neuronal signaling, and has been implicated in neuroprotection. In addition, this fatty acid is required for retinal pigment epithelium cell (RPE) functional integrity. Here we provide an overview of the recent elucidation of a specific mediator generated from DHA that contributes at least in part to its biological significance. In oxidative stress-challenged human RPE cells and rat brain undergoing ischemia-reperfusion, 10,17S-docosatriene (neuroprotectin D1, NPD1) synthesis evolves. In addition, calcium ionophore A23187, IL-1beta, or the supply of DHA enhances NPD1 synthesis. A time-dependent release of endogenous free DHA followed by NPD1 formation occurs, suggesting that a phospholipase A2 releases the mediator's precursor. When NPD1 is infused during ischemia-reperfusion or added to RPE cells during oxidative stress, apoptotic DNA damage is down-regulated. NPD1 also up-regulates the anti-apoptotic Bcl-2 proteins Bcl-2 and BclxL and decreases pro-apoptotic Bax and Bad expression. Moreover, NPD1 inhibits oxidative stress-induced caspase-3 activation. NPD1 also inhibits IL-1beta-stimulated expression of COX-2. Overall, NPD1 protects cells from oxidative stress-induced apoptosis. Because photoreceptors are progressively impaired after RPE cell damage in retinal degenerative diseases, understanding of how these signals contribute to retinal cell survival may lead to the development of new therapeutic strategies. Moreover, NPD1 bioactivity demonstrates that DHA is not only a target of lipid peroxidation, but rather is the precursor to a neuroprotective signaling response to ischemia-reperfusion, thus opening newer avenues of therapeutic exploration in stroke, neurotrauma, spinal cord injury, and neurodegenerative diseases, such as Alzheimer disease, aiming to up-regulate this novel cell-survival signaling.

Cellular and molecular events in corneal wound healing: significance of lipid signalling

Alterations in the normal healing process after corneal injury can produce undesirable outcomes that range from corneal haze to ulceration and perforation. Lipids play important roles in the complex inflammatory processes that occur after corneal wounding. While some lipid mediators, such as the lipoxygenase derivatives of arachidonic acid, 12-hydroxyeicosatetraenoic acid (12[S]-HETE and 15[S]-HETE), act as second messengers to promote cell proliferation and are possibly involved in the synthesis of other molecules that suppress inflammation, others, such as platelet-activating factor (PAF), exert their actions through specific receptors, play key roles during sustained corneal inflammation (as might occur with chemical burns), and contribute to tissue destruction and neovascularization. PAF is also a strong inducer of selective metalloproteinases (MMPs) that degrade the extracellular matrix. The use of a new PAF antagonist has shown great promise for the treatment of diffuse lamellar keratitis (DLK) and alkali-burned corneas.

Cytidine 5'-diphosphocholine (CDP-choline) in stroke and other CNS disorders

Brain phosphatidylcholine (PC) levels are regulated by a balance between synthesis and hydrolysis. Pro-inflammatory cytokines such as tumor necrosis factor-alpha (TNF-alpha) and interleukin-1 (IL-1alpha/beta) activate phospholipase A(2) (PLA(2)) and PC-phospholipase C (PC-PLC) to hydrolyze PC. PC hydrolysis by PLA(2) releases free fatty acids including arachidonic acid, and lyso-PC, an inhibitor of CTP-phosphocholine cytidylyltransferase (CCT). Arachidonic acid metabolism by cyclooxygenases/lipoxygenases is a significant source of reactive oxygen species. CDP-choline might increase the PC levels by attenuating PLA(2) stimulation and loss of CCT activity. TNF-alpha also stimulates proteolysis of CCT. TNF-alpha and IL-1beta are induced in brain ischemia and may disrupt PC homeostasis by increasing its hydrolysis (increase PLA(2) and PC-PLC activities) and inhibiting its synthesis (decrease CCT activity). The beneficial effects of CDP-choline may result by counteracting TNF-alpha and/or IL-1 mediated events, integrating cytokine biology and lipid metabolism. Re-evaluation of CDP-choline phase III stroke clinical trial data is encouraging and future trails are warranted. CDP-choline is non-xenobiotic, safe, well tolerated, and can be considered as one of the agents in multi-drug treatment of stroke.

Synaptic and vascular associations of neurons containing cyclooxygenase-2 and nitric oxide synthase in rat somatosensory cortex

Cyclooxygenase-2 (COX-2) is a rate-limiting enzyme for prostanoid synthesis that is present in cortical pyramidal neurons and highly implicated in control of cerebral blood flow during neural activity. We examined the electron microscopic localization of COX-2 and neuronal nitric oxide synthase (nNOS), a functionally related enzyme, in the somatosensory cortex of rat brain to determine the relevant functional sites. COX-2 immunoreactivity was detected in significantly more somatodendritic than axonal profiles, while nNOS was more often seen in axon terminals. The dendritic COX-2 was localized to endomembranes near synaptic inputs from axon terminals, some of which contained nNOS. Conversely, COX-2 terminals formed asymmetric, excitatory-type synapses with dendrites containing nNOS. The dendritic and axonal profiles containing COX-2 as well as those containing nNOS were minimally separated from penetrating arterioles and capillaries by filamentous glial processes. The perivascular COX-2 labeled terminals were among those that also formed axo-dendritic synapses, suggesting that the release of prostanoids and/or excitatory transmitters from a single terminal may simultaneously affect neuronal activity and cerebral blood flow. Thus, COX-2 has a compartmental distribution in somatosensory cortical neurons consistent with the local neuronal synthesis of prostanoids that are involved in neurovascular coupling and whose actions are modulated by nitric oxide.

Oxidative stress-induced death in the nervous system: cell cycle dependent or independent?

Neuronal death, attributable to perturbed redox homeostasis, is the underlying factor in many acute and chronic neurological disorders. The mechanisms employed by oxidatively stressed neurons to commit to cell death pathways are beginning to be characterized, but this is hampered by a lack of good models that extrapolate readily to redox-dependent neuronal death paradigms. In this Mini-Review, we discuss mechanisms by which oxidative stress can result in neurodegeneration. We examine evidence on which terminally differentiated neurons might commit to death under conditions of oxidative stress. In some cases, death may be linked to an aberrant and uncoordinated reentry into the cell cycle and mitotic catastrophe. Other evidence suggests that cell cycle reentry is not mandatory for death execution. Rather, the reexpression of cell cycle proteins may induce apoptotic pathways in a cell cycle-independent manner. In contrast to these models, there is also evidence that oxidative neuronal death is independent of cell cycle proteins. We conclude that oxidative stress-induced neuronal death may be promoted via several pathways, which may be cycle protein dependent or independent. The determining factor for which or how many pathways are induced appears to be context dependent and determined by the level and duration of oxidative stress.

Effects of hyperglycemia and hypercapnia on lipid metabolism during complete brain ischemia

Ischemic damage is greatly enhanced by preischemic hyperglycemia or hypercapnia, which affects many intracellular responses including protein kinase C (PKC) translocation. We explored whether hyperglycemic or hypercapnic ischemia affects lipid metabolism, especially ischemia-induced release of free fatty acids (FFAs) and diacylglycerols (DAGs). A change in intraischemic level of acidosis was induced either by injecting glucose (hyperglycemic, HG) or by adding CO(2) (hypercapnic, HC). Complete cerebral ischemia was induced, and the brain was frozen in situ after 3, 5, and 10 min at 37 degrees C. Frontoparietal neocortex was dissected for FFA and DAG lipid analysis by thin-layer chromatography and gas-liquid chromatography. Significant differences were shown between normoglycemic and either hypercapnic or hyperglycemic values for individual and total FFAs. A significant delay in the release of FFA in ischemia with hyperglycemia or hypercapnia was observed. Significant differences were also shown in individual DAG-acyl groups and total DAGs. Hyperglycemic or hypercapnic ischemia resulted in a significant decrease of DAG at 10 min of ischemia. This was unexpected because a previous study showed that PKC translocation was significantly enhanced under similar condition at this time point. Upon cellular depolarization, massive influx of calcium and FFA accumulation may decrease the PKC dependence of DAG for translocation. In addition, PKC activation may lead to a negative feedback inhibition of phospholipase C.

Docosahexaenoic acid complexed to albumin elicits high-grade ischemic neuroprotection

BACKGROUND AND PURPOSE

High-dose human albumin therapy is strongly neuroprotective in models of brain ischemia and trauma and is currently being studied in a pilot-phase clinical stroke trial. Among its actions in ischemia, albumin induces the systemic mobilization of n-3 polyunsaturated fatty acids and may help to replenish polyunsaturated fatty acids lost from neural membranes.

METHODS

We complexed 25% human albumin to docosahexaenoic acid (DHA; 22:6n-3) and compared its neuroprotective efficacy with that of native albumin in rats with 2-hour focal ischemia produced by intraluminal suture-occlusion of the middle cerebral artery.

RESULTS

In animals treated with DHA-albumin, 0.63 g/kg, the improvement in neurobehavioral scores at 72 hours significantly exceeded that of other treatment groups, and the extent of histological protection (86% reduction in cortical infarction) was highly significant and tended to surpass the degree of cortical protection produced by native albumin at 1.25 g/kg (65%). DHA-albumin 0.63 g/kg, but not native albumin, also significantly reduced subcortical infarction and markedly diminished brain swelling. Lipidomic analysis of DHA-albumin-treated postischemic brains revealed a large accumulation of the neuroprotective DHA metabolite, 10,17S-docosatriene, in the ipsilateral hemisphere.

CONCLUSIONS

The high-grade neuroprotection afforded by the DHA-albumin complex at relatively low albumin doses is clinically advantageous in that it might reduce the likelihood of acute intravascular volume overload and congestive heart failure sometimes induced when patients with compromised cardiovascular function are treated with high-dose albumin.

Site-Specific Differences in Fatty Acid Composition of Dendritic Cells and Associated Adipose Tissue in Popliteal Depot, Mesentery, and Omentum and Their Modulation by Chronic Inflammation and Dietary Lipids

BACKGROUND

This study explores the role of lymphatics-associated adipocytes in determining the lipid composition of dendritic cells.

METHODS AND RESULTS

Adult male rats were fed plain chow, or chow supplemented with 20% sunflower or fish oil. Chronic local inflammation was induced by subcutaneous injection of 20 microg lipopolysaccharide three times a week for 2 weeks near the popliteal lymph nodes. Chemokine-stimulated dendritic cells were collected over 4 hours from popliteal and mesenteric lymph nodes, and perinodal and other samples of mesenteric, popliteal, and omental adipose tissue. Fatty acids extracted from triacylglycerols and/or phospholipids were separated and quantified by gas chromatography from each sample of dendritic cells and intracellular lipids, membranes, stroma and isolated adipocytes from the adipose tissue. Dendritic cells from lymph nodes and adipose tissue samples differed in fatty acid composition, and were modulated by diet. The site-specific differences of dendritic cells correlated with those of the contiguous adipocytes. Chronic mild stimulation altered the lipid composition of dendritic cells near the inflamed site and elsewhere; changes were minimal after the fish-oil diet. The composition of adipocyte triacylglycerol and phospholipid fatty acids also changed near the stimulation site in ways that counteracted alterations induced by the experimental diets.

CONCLUSIONS

Fatty acids in dendritic cells differed with anatomical site, and were determined by the adjacent adipocytes, which actively regulated their own lipid composition. These findings demonstrated functional bases for the anatomical associations between adipose and lymphoid tissues and may be a mechanism by which dietary lipids modulate the immune system.

Targeted disruption of PSD-93 gene reduces platelet-activating factor-induced neurotoxicity in cultured cortical neurons

PSD-93, a molecular adaptive protein, binds to and clusters the N-methyl-D-aspartate (NMDA) receptor and assembles a specific set of signaling proteins (for example neuronal nitric oxide synthase, nNOS) around the NMDA receptor at synapses in the central nervous system. This suggests that PSD-93 might mediate many NMDA receptor-dependent physiological and pathophysiological functions. We report here that PSD-93 colocalizes and interacts with the NMDA receptor and neuronal nitric oxide synthase in cultured cortical neurons. Targeted disruption of PSD-93 gene significantly prevented NMDA receptor-nitric oxide signaling-dependent neurotoxicity triggered via platelet-activating factor (PAF) receptor activation. In addition, the deficiency of PSD-93 markedly attenuated platelet-activating factor-induced increase in cyclic guanosine 3',5'-monophosphate (cGMP) and prevented platelet-activating factor-promoted formation of NMDA receptor-neuronal nitric oxide synthase complex. These findings indicate that PSD-93 is involved in the NMDA receptor--nitric oxide-mediated pathological processing of neuronal damage triggered via platelet--activating factor receptor activation. Since platelet-activating factor is a potent neuronal injury mediator during the development of brain trauma, seizures, and ischemia, the present work suggests that PSD-93 might contribute to molecular mechanisms of neuronal damage in these brain disorders.

Docosahexaenoic acid protects from dendritic pathology in an Alzheimer's disease mouse model

Learning and memory depend on dendritic spine actin assembly and docosahexaenoic acid (DHA), an essential n-3 (omega-3) polyunsaturated fatty acid (PFA). High DHA consumption is associated with reduced Alzheimer's disease (AD) risk, yet mechanisms and therapeutic potential remain elusive. Here, we report that reduction of dietary n-3 PFA in an AD mouse model resulted in 80%-90% losses of the p85alpha subunit of phosphatidylinositol 3-kinase and the postsynaptic actin-regulating protein drebrin, as in AD brain. The loss of postsynaptic proteins was associated with increased oxidation, without concomitant neuron or presynaptic protein loss. n-3 PFA depletion increased caspase-cleaved actin, which was localized in dendrites ultrastructurally. Treatment of n-3 PFA-restricted mice with DHA protected against these effects and behavioral deficits and increased antiapoptotic BAD phosphorylation. Since n-3 PFAs are essential for p85-mediated CNS insulin signaling and selective protection of postsynaptic proteins, these findings have implications for neurodegenerative diseases where synaptic loss is critical, especially AD.

Cyclooxygenase-2 (COX-2) in Inflammatory and Degenerative Brain Diseases

Cyclooxygenase (COX) catalyses the first committed step in the synthesis of prostanoids, a large family of arachidonic acid metabolites comprising prostaglandins, prostacyclin, and thromboxanes, and is a major target of non-steroidal anti-inflammatory drugs (NSAIDs). COX exists as constitutive and inducible isoforms. COX-2 is the inducible isoform, rapidly expressed in several cell types in response to growth factors, cytokines, and pro-inflammatory molecules. Since its discovery in the early 1990s, COX-2 has emerged as a major player in inflammatory reactions in peripheral tissues. By extension, COX-2 expression in brain has been associated with pro-inflammatory activities, thought to be instrumental in neurodegenerative processes of several acute and chronic diseases. However, 2 major aspects should be borne in mind. First, in the central nervous system, COX-2 is expressed under normal conditions and contributes to fundamental brain functions, such as synaptic activity, memory consolidation, and functional hyperemia. Second, "neuroinflammation" is a much more controlled reaction than inflammation in peripheral tissues, and in many cases is triggered and sustained by activation of resident cells, particularly microglia. In spite of the intense research of the last decade, the evidence of a direct role of COX-2 in neurodegenerative events is still controversial. This article will review new data in this area, focusing on some major human neurological diseases, such as multiple sclerosis, amyotrophic lateral sclerosis, Parkinson disease, Creutzfeldt-Jakob disease, and Alzheimer disease. Furthermore, the emerging role of COX-2 in behavioral and cognitive functions will be discussed.

Effects of dietary omega-3 polyunsaturated fatty acids on brain gene expression

Polyunsaturated fatty acids (PUFA) are essential structural components of the central nervous system. Their role in controlling learning and memory has been well documented. A nutrigenomic approach with high-density microarrays was used to reveal brain gene-expression changes in response to different PUFA-enriched diets in rats. In aged rats fed throughout life with PUFA-enriched diets, genes with altered expressions included transthyretin, alpha-synuclein, and calmodulins, which play important roles in synaptic plasticity and learning. The effect of perinatal omega-3 PUFA supply on gene expression later in life also was studied. Several genes showed similar changes in expression in rats fed omega-3-deficient diets in the perinatal period, regardless of whether they or their mothers were fed omega-3 PUFA-sufficient diets after giving birth. In this experiment, among the down-regulated genes were a kainate glutamate receptor and a DEAD-box polypeptide. Among the up-regulated genes were a chemokine-like factor, a tumor necrosis factor receptor, and cytochrome c. The possible involvement of the genes with altered expression attributable to different diets in different brain regions in young and aged rats and the possible mode of regulatory action of PUFA also are discussed. We conclude that PUFA-enriched diets lead to significant changes in expression of several genes in the central nervous tissue, and these effects appear to be mainly independent of their effects on membrane composition. The direct effects of PUFA on transcriptional modulators, the downstream developmentally and tissue-specifically activated elements might be one of the clues to understanding the beneficial effects of the omega-3 PUFA on the nervous system.

Eicosanomics: targeted lipidomics of eicosanoids in biological systems

Recent advancements in mass spectrometry, especially the development of electrospray tandem mass spectrometry (ESI/LC/MS2) and matrix-assisted laser desorption time-of-flight mass spectrometry (MALDI/TOF), have greatly facilitated analysis of complex biomolecules. It has now become possible to profile, in relatively short periods of time, large multicomponent groups of compounds biosynthesized by biological systems. The efficiency and accuracy of analysis have led to the development of new concepts of mass spectrometric profiling, mapping, and imaging. Profiling of proteins in biological material (proteomics) has become a widely accepted strategy for identification of mechanisms involved in the biochemistry of disease processes, and has become a novel tool for unraveling new drug targets. Evolution of proteomics has relied on ESI/LC/MS2 and MALDI/TOF, techniques that are also useful in the novel area of quantitative proteomics.

Acyl-CoA synthetase 2 overexpression enhances fatty acid internalization and neurite outgrowth

During neurodevelopment neurons increase phospholipid synthesis to generate additional plasma membrane that makes up the growing neurites. Compared with most cell types, neurons contain a high percentage of the polyunsaturated fatty acids (PUFAs) arachidonic acid (AA) and docosahexaenoic acid (DHA). By utilizing PC12 cell lines as a model neuronal cell line, we examined the internalization rate of AA, DHA, and non-essential oleic acid (OA), as well as their effects on neurite outgrowth. When wild type cells were differentiated, the rate of AA and DHA internalization increased 50% more than the rate of OA internalization. When media were supplemented with AA or DHA, the average neurite length was increased by approximately 40%, but supplementation with the same amount of OA had no effect. We also increased the levels of acyl-CoA synthetase-1 (ACS1) and ACS2 proteins to determine whether they contribute to PUFA internalization or neurite outgrowth. Overexpression of ACS1 increased the rate of OA internalization by 55%, and AA and DHA uptake was increased by 25%, but there was no significant change in neurite outgrowth. In ACS2-overexpressing cells, in contrast, the rate of OA internalization increased by 90%, AA by 115%, and DHA by 70%. The average aggregate neurite length in ACS2-overexpressing cells was increased by approximately 40% when the media were supplemented with PUFAs, but there was no change with OA supplementation. Taken together, these results support the hypotheses that ACSs are rate-limiting for fatty acid internalization and that ACS2 enhances neurite outgrowth by promoting PUFA internalization.

Prostaglandins are powerful inducers of NGF and BDNF production in mouse astrocyte cultures

We found that prostaglandin (PG) D(2) and PGE(2), which are major PGs in the brain of mammals, powerfully induced the secretion of nerve growth factor (NGF) from cultured mouse astrocytes; PGE(2) or PGD(2) induced an approximately 12- or 19-fold increase in NGF secretion after a 24-h incubation, respectively. Moreover, it was found that the sequential metabolites of PGD(2), PGJ(2), Delta(12)-PGJ(2), and 15-deoxy-Delta(12,14)-PGJ(2), induced the NGF secretion to the culture medium strikingly (60-98-fold of the control after a 24-h incubation). NGF secretion induced by the J(2) series of PGs was accompanied by the increased expression of NGF mRNA. These PGs also stimulated the secretion/synthesis of brain-derived neurotrophic factor (BDNF). Our findings suggest that PGs play a neuroprotective role by inducing NGF and BDNF production in the central nervous system.